The work proposed is a continuation of studies on transfer RNA (tRNA) of red blood cell precursors, with particular interest in a possible role of tRNA in the regulation of the rate and amount of hemoglobin synthesis. Work includes the determination of the tRNA content of reticulocytes from various sources and the use of a cell free system to study the effect of limiting tRNA on the rate of hemoglobin synthesis and to study site specific incorporation of amino acids into hemoglobin by purified tRNA species.